Ground-Source Heat Pumps
Otherwise known as earth-energy systems, the ground-source heat pump can pull heat from ground water the earth to heat your home. The earth and groundwater may then be used to remove heat from the home in the summer.
In order to remove the heat from the earth, either ground water or a solution made with antifreeze will be heated by the heat pump and then the heat is transferred to the house in the form of warm air. When it is summer, the heat will be taken from the air in the house and directed to the earth through ground water or the antifreeze solution.
Also available is a direct-expansion (DX) earth-energy system, which uses refrigerant rather than antifreeze.
How Does the System Work?
There are two parts to the earth-energy system. One is a system of piping underground, outside, and the other is a heat pump inside. The whole heat pump unit is inside the home, which is different from an air-source heat pump, in which one heat exchanger and possibly the compressor are placed outside.
The piping part of the system is placed in a loop shape, and the circuit may be either open or closed. If it is open, the water will be extracted by a well and will be sent straight to a heat exchanger. From there, it will be discharged into a pond or other body of water that is visible above ground, or to a different well underground.
If it is closed, the piping is all connected underground. After the antifreeze or refrigerant flows through the heat pump’s refrigeration system and is cooled to several degrees below the temperature of the soil outside. It will then circulate through the piping and absorb the heat from the soil.
The Heating Cycle
During the heating cycle, after the ground water, antifreeze solution or refrigerant has become warmer from circulating under the soil, it flows back into the heat pump unit in the home. If it is a system that uses ground water or an antifreeze mixture, then it will be passed through the primary heat exchanger, which is filled with refrigerant. If it is a DX system, the refrigerant will enter the compressor without the need for a heat exchanger.
The refrigerant absorbs the heat and begins to boil, which transforms it into a low-temperature vapour. If it is an open system, the ground water will be pumped out into a pond or well. If it is a closed-loop system, the antifreeze mixture or refrigerant will be pumped out to the underground piping system to be reheated.
A reversing valve is implemented to guide the vapour to the compressor, which will reduce the vapour’s volume and make it heat up. After the vapour turns to hot gas, it will travel to the condenser coil and the heat is blown over the coil, and is pushed through the duct system, heating the home.
Once the heat has passed through, the refrigerant will pass through the expansion device and the pressure and temperature are lowered before the air goes back to the first heat exchanger, or, in a DX system, to the ground. Then the cycle will start over.
Domestic Hot Water
A heat exchanger can be used to pull the heat out of hot refrigerant when it comes out of the compressor. The name for this is “desuperheater.” The water heater for the home will then pump water through a coil, so that some of the water is heated.
Since there is plenty of heat to spare in the summer, the water heater will be more efficient during that season. The summer cooling mode can also be used during mild weather, even though the heat pump is above the balance point during that time.
The whole machine will switch to provide domestic hot water (DHW) when necessary. This makes it easier to heat the water since the compressor is inside. This results in more hours of surplus heating capacity.
The Cooling Cycle
Not surprisingly, the cooling cycle is pretty much like the heating cycle, except in reverse. The refrigerant can be set to flow the opposite way by flipping the reversing valve. The refrigerant will pull heat from the air inside the home.
The hot air will be transferred in a DX system, or be directed to the groundwater or antifreeze mix, then pumped into a water body or well, or into pipes under the ground, depending on whether the system is open- or closed-loop. Some of the extra heat can be used to warm up domestic hot water.
In earth-energy systems, a defrost cycle is not needed. This is due to the fact that temperatures underground remain steady far more than air temperatures. Also, the heat pump is in the house, so frost is not a problem.
The System’s Parts
There are three main parts of an earth-energy system – the heat pump unit, liquid heat exchange and air delivery system. How these parts work together depends on the design.
In a self-contained unit, the blower, compressor, heat exchanger and condenser coil will all be in one cabinet, while in a split system, the coil will be added on to a forced-air furnace, and use the blower and furnace that are already available.
Energy Efficiency
There are various levels of energy efficiency, depending on the type of earth-energy system. Those that are built as groundwater or open systems have a range of COP ratings between 3.6 and 5.2, and a range of cooling ratings between 16.2 and 31.1. Those that are built as closed-loop applications have a range of COP ratings between 3.1 and 4.9 and EER ratings between 13.4 and 25.8.
Earth-energy systems have improved a great deal, resulting in higher efficiency. For the lower-efficiency systems, earth-energy systems use either single-speed rotary or reciprocating compressors, while mid-range units use scroll compressors or advanced reciprocating compressors. High-efficiency units are typically equipped with two-speed compressors, variable-speed indoor fan motors, or both.
To qualify as Canada ENERGY STAR high efficiency units, EESs must meet or exceed certain specifications, including that they are 10 to 50 percent more efficient than regular models.
Sizes of EESs
An EES can offer consistent output, so it can heat the air in an area, and also have enough energy left over to heat up water as well. Air-source heat pumps should not normally be counted on to heat an entire house, but rather should take care of about 60-70 percent of the space and water heating needs. When the most energy is needed, during the coldest weather, for example, another source of heat may be needed.
EESs that are equipped with variable speed are capable of almost all heating and cooling loads when on low speed. High speed will only be needed for higher heating needs.
Designs of EESs
EESs will require either a pond or well, or a loop system, in order to function properly.
Open Systems
An open system is designed to use a well as a heat source. Groundwater will be extracted into a heat pump and then the heat is pulled out. The water is then released into a body of water, such as a stream, pond, etc. This is not always a legal option.
Another way the water can be dispersed is into a rejection well, as long as it is large enough to hold the water. It should be built, installed or inspected by a professional to ensure that there will not be any negative effect on the environment. The heat pump should only change the temperature of the water, so there should not be an issue with pollution.
The water volume needed in an open system will depend on the heat pump size and manufacturer’s specifications. The measuring unit is usually litres per second. The well and pump must be capable of supplying enough water for all your home needs.
If water quality from which a unit is pulling water is not clean, it can cause issues with the entire unit, like clogging. Besides particles and debris, excess acidity and iron can be problems, as can overly hard water. A professional contractor should be able to test the water and determine it is good enough or not.
The water must also have a consistent temperature, enough above freezing, to supply the pump with water, even during the coldest days of the year. Again, a professional should be able to help make this determination. Homeowners should also check on any licensing requirements before installing an EES.
Closed-Loop Systems
In a closed-loop system, the heat comes from within the ground, where there is plastic pipe installed. In DX systems the piping is made of copper. The pipes are attached to an indoor heat pump and antifreeze mix or refrigerant is circulated through the circuit. Open systems will bring the water in from a well, while in the closed-loop system, the water flows through the pipe.
There are two ways the pipes may be arranged. Pipes may be set up vertically, and this is typically used when there is a lack of space. The piping will be inserted in u-shaped loops, and the holes do not need to be very large. With DX systems, the holes can be even smaller, and this can save money when it comes to drilling costs. All the holes should be backfilled, and the dirt pressed down into the holes.
When there is plenty of land to work with, pipes will usually be placed horizontally. The pipes will be installed in trenches. Normally, in a horizontal design will be set up with two pipes beside one another in a trench, or the pipes may be laid out in a spiral, or with four to six pipes per trench.
The type of piping used depends on the system. As mentioned earlier, DX systems employ copper pipes. Other systems that require the use of antifreeze solution will be set up with 100 polyethylene or polybutylene pipes with joints that are fused thermally, not with glue, clamps or barbed fittings. The advantages to these types of pipes are that they are not affected by chemicals and they will last for decades without leaking, if they are properly installed.
It is always best to hire a professional for installation of these systems. Thermal fusing and ensuring that the earth has proper contact with the piping are important, and an amateur may not be able to accomplish it. If things are not set up well, the system will not operate at maximum ability.
Installation of EES
Whenever an earth-energy system is installed, it should be done professionally, from the design to the installation, and beyond. After installation, proper care and operation are necessary to ensure that Canadian Standards Association regulations are being met, and that the system is operating at its top capability.
EESs will vary on cost, but the price to install may be double that for a gas, oil, or electric furnace and air conditioner. The majority of the expense comes from the ground collectors that must be placed, and the amount can be affected by whether it is an open or closed-loop system. Ductwork within the home can be another issue. The style of home and other factors can make ductwork installation more difficult. Either way, this should be done by a professional.
The good news is that after the initial installation costs, an EES will most likely save consumers enough money over the next few years to make up for the extra expense at the beginning. There are also often incentive plans available for those who opt to have an EES installed.
The Upside of Earth-Energy Systems
1. Saving Energy – EESs can drastically cut heating and cooling costs, by more than half in comparison with regular electric furnaces. Since the heating source comes from underground pipes where the temperature is far more consistent than that of the air. Consequently, it does not have to work as hard, and savings can result. Of course the actual amount of money saved will depend on the overall climate, the efficiency of the unit and size of the heat pump, fuel costs versus electricity costs and more.
2. Maintenance – Since EESs do not need much in the way of maintenance, the costs in this area are pretty low. The most important tasks are cleaning and replacing fans and filters, so that air flow will not be adversely affected, and cleaning and inspecting ductwork regularly to avoid obstructions. Likewise, the vents and registers should always have a clear path for air to flow through into the home. In open systems, the heat exchanger must be checked regularly for deposits.
3. Low Cost to Operate – EESs do not require as much energy to operate, and therefore costs for running the systems is often lower overall. This is because it is not necessary to use gas or oil. However, for those who live in an area where electricity costs more, the operating costs will be higher, due to the electricity needed for running the heat pump.
4. Heating Water – With a desuperheater, which uses excess heat that has been extracted to heat water, money can be saved on water heater operation. This can reduce the water heating bill quite a bit.
5. Longevity – While an average EES lasts around 20 years or more, they are also usually covered by warranties, at least for the first year, but this factor, of course, varies. Nevertheles, the EES will often last longer than the average air-source heat pump because there is not as much environmental exposure to the compressor.
Thinking about installing a heat pump for your home? Consult these HVAC professionals:
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[column size=”1/3″]Gazifère
Heating[/column]
[column size=”1/3″]Address: 706 Boulevard Gréber
Gatineau, QC J8V 3P8
Phone: (819) 771-8321
Fax: (819) 776-8827
Email: info@gazifere.com
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